In the field of dentistry, one method for obturating root canal cavities involves injecting heated thermoplastic material, typically gutta-percha, into the dental cavity with a dental thermoplastic injection device. The injection device is typically a syringe-like instrument having a hollow needle through which the thermoplastic is ejected when the needle is inserted into the dental cavity. The needle is of high thermal conductivity material such as gold, silver, copper or aluminum to assume thermal conductance from a heater in the injection device to maintain the fluidity of the gutta-percha in the needle. See U.S. Pat. No. 4,357,136.
The needle is usually formed from two separate pieces which are joined together. The first piece is a narrow elongate needle portion made of the high thermal conductivity metal such as silver about 1 inch long with a constant diameter between 18 and 30 gauge. The second piece is a threaded hub portion which is brazed to the needle portion. The hub portion allows the needle to be attached to the injection device by screwing the hub portion into the body of the injection device. A drawback with this design is that the joint between the needle and the hub portions may break when the needle is bent within a convoluted dental cavity. Another drawback with the design is that the process for manufacturing the needle is relatively slow and expensive.